Patent GB-1282221-A (GB)
Title: Arrangement for supplying a plurality of groups of loads from a common power source
IPC: H02J3/14
Filed: 1970-01-14
Abstract: 1282221 Supply systems for nuclear reactor control rod mechanisms WESTINGHOUSE ELECTRIC CORP 14 Jan 1970 [13 Feb 1969] 1813/70 Heading H2H [Also in Division G6] A plurality of groups of load elements are supplied from a common three phase A.C. source through a rectifier which is controlled to maintain desired currents through the elements as set by a plurality of reference current signals and which supplies the load elements through a plurality of normally-open controlled electronic switches, these switches corresponding in number to the number of groups or load elements and being closed by control signals so that the groups are sequentially energized in a predetermined manner. The invention is applied to insert and withdraw the control rods of a nuclear reactor and, as shown in Fig. 1, the stationary, lift and movable coils of the rod jack mechanisms constitute the load elements and are arranged in groups 12, 14, 16; 22, 24, 26 and 32, 34, 36 which are supplied from a three phase source 40 through rectifiers 42, 46, 50, 52, 54 controlled in accordance with reference current signals produced by a reference source 62. These rectifiers maintain the coil current constant at a number of sequential reference current values, in the manner described in Specification 1,282,222. Sequential switching for the lift and movable coils is provided by the control units 66, 76 of which the former is shown in Fig. 2. The control rods are divided into three groups respectively associated with the coil groups 12, 22, 32; 14, 24, 34 and 16, 26, 36. A typical withdrawal operation comprises, for the first group of rods, energization of the movable coils 32, de-energization of stationary coils 12, energization of lift coils 22 to withdraw the rods one increment, re-energization of stationary coils 12 and finally de-energization of the coils 22, 32. Similar operations are then carried out on the coil groups 14, 24, 34 and 16, 26, 36. The lift coils are arranged in groups 22<SP>1</SP>, 241, 26<SP>1</SP> (Fig. 2) each coil being in series with a respective thyristor 109, 115 or 121, which are controlled in groups corresponding to the coils. The movable coils are also arranged in groups, but only one thyristor per group is provided, Fig. 3 (not shown). The coil currents are sensed at points 141 to control the rectifier 101 which corresponds to the rectifier 42 in Fig. 1. The firing signals for the thyristors of the units 66, 76 are provided by the circuit shown in Fig. 4, which comprises an oscillator 180 whose output is applied to groups of firing means 192, 220, 222 according to the positions of switches 181, 213 of the mercury wetted contact type. The coil currents are monitored (at points 147, 149, 151 in Fig. 2) and are compared with reference values to provide an alarm signal in the event of a fault, Fig. 5 (not shown). Switches 181, 213 are controlled by a logic circuit, Fig. 6A (not shown), which circuit actuates the coils in the desired sequence and inhibits the protection system during conditions of coil energization, Fig. 6B (not shown). Switches 191, 193, 195 are provided to enable the rods to be re-aligned.